The practice of ellipsometry is well established as a non-destructive approach to determining characteristics of material systems, and can be applied in real time process control. The topic is generally well described in a number of publication, one such publication being a review paper by Collins, titled “Automatic Rotating Element Ellipsometers: Calibration, Operation and Real-Time Applications”, Rev. Sci. Instrum, 61(8) (1990).
In general, modern practice of ellipsometry typically involves causing a spectroscopic beam of electromagnetic radiation, in an imposed, known, state of polarization, to interact with a material system at one or more angle(s) of incidence with respect to a normal to a surface thereof, in a plane of incidence. (Note, a plane of incidence contains both a normal to a surface of an investigated material system and the locus of said beam of electromagnetic radiation). Changes in the polarization state of said beam of electromagnetic radiation which occur as a result of said interaction with said material system are indicative of the structure and composition of said material system. The practice of ellipsometry utilizes said changes in polarization state by proposing a mathematical model of the ellipsometer system and the material system investigated by use thereof, obtaining experimental data by application of the ellipsometer system, and applying square error reducing mathematical techniques (eg. regression), to the end that parameters in the mathematical model which characterize the material system are evaluated so that the obtained experimental data, and values calculated by use of the mathematical model have a “best match” relationship.
A goal in ellipsometry is to obtain, for each wavelength in, and angle of incidence of said beam of electromagnetic radiation caused to interact with a material system, material system characterizing PSI and DELTA values, (where PSI is related to a change in a ratio of magnitudes of orthogonal components rp/rs in said beam of electromagnetic radiation, and wherein DELTA is related to a phase shift entered between said orthogonal components rp and rs, caused by interaction with said material system;PSI=|rp/rs|; andDELTA=(Δrp−Δrs).
As alluded to, the practice of ellipsometry requires that a mathematical model be derived and provided for a material system and for the ellipsometer system being applied. In that light it must be appreciated that an ellipsometer system which is applied to investigate a material system is, generally, sequentially comprised of:                a. a Source of a beam electromagnetic radiation;        b. a Polarizer element;        c. optionally a compensator element;        d. (additional element(s) such as lens(es), beam directing means, and/or windows such as in vacuum chambers);        e. a material system;        f. (additional element(s) such as lens(es), beam directing means, and/or windows such as in vacuum chambers);        g. optionally a compensator element;        h. an Analyzer element; and        i. a Detector System.Each of said components b.-i. must be accurately represented by a mathematical model of the ellipsometer system along with a vector which represents a beam of electromagnetic radiation provided from said source of a beam electromagnetic radiation, Identified in a. above)        
It is noted that various ellipsometer configurations provide that a Polarizer, Analyzer and/or Compensator(s) can be rotated during data acquisition, and are describe variously as Rotating Polarizer (RPE), Rotating Analyzer (RAE) and Rotating Compensator (RCE) Ellipsometer Systems.
Continuing, as disclosed in Pending application Ser. No. 09/583,229, and U.S. Pat. No. 6,034,777, where an ellipsometer system is applied to investigate a small region of a material system present, it must be appreciated that the beam of electromagnetic radiation can be convergently entered thereto through an input lens, and, optionally, exit via a re-collimating output lens. In effect this adds said input, (and output), lenses as elements in the ellipsometer system as “additional elements”, (eg. identified in d. and f. above), which additional elements must be accounted for in the mathematical model. If this is not done, material system representing parameters determined by application of the ellipsometer system and mathematical regression, will have the effects of said input, (and output), lenses at least partially correlated thereinto, much as if the input and, (output lenses), were integrally a part of the material system. Further, while lenses, including multi-element lenses utilized the present invention system in ellipsometric settings are typically relatively less birefringent and chromatically dispersive than are, for instance, electromagnetic beam directing mirror systems, in the case where a multi-element input and/or output optical element(s) demonstrates birefringence, the described approach can further comprise a method of accurately evaluating parameters in parameterized equations in a mathematical model of a system of spatially separated input and output elements, (herein beneficially, demonstratively, identified as lenses), as applied in an ellipsometry or polarimetry setting. Said parameterized equations enable, when parameters therein are properly evaluated, independent calculation of retardation entered by each of said multi-element input lens and said multi-element output lens to, or between, orthogonal components of a beam of electromagnetic radiation caused to pass through said input and output lenses. This provides utility in the form of enabling the breaking of correlation between retardation entered between orthogonal components in a spectroscopic electromagnetic beam by input and output lenses and by a material system under investigation. (It is to be understood that at least one of said multi-element input and output lenses in an ellipsometer is often at least somewhat birefringent even though it is quasi-achromatic regarding focal length over a relativley wide wavelength range).
Said Pending application Ser. No. 09/583,229, and U.S. Pat. No. 6,034,777, teach methodology for breaking correlation between retardation effects caused by multi-element input and/or output lenses in an ellipsometer system, and retardation effects caused by an adjacent, otherwise ellipsometrically undistinguishable material system being investigated comprises, in any functional order, the steps of:
a. providing spatially separated input and output optical element (eg. lenses which perform as focusing/defocusing means), at least one of said input output lenses demonstrating birefringence when a beam of electromagnetic radiation is caused to pass therethrough, there being a means for supporting a material system positioned between said input and output lenses;
b. positioning an ellipsometer system source of electromagnetic radiation and an ellipsometer system detector system such that in use a beam of electromagnetic radiation provided by said source of electromagnetic radiation is caused to pass through said input lens, interact with said material system in a plane of incidence thereto, and exit through said output lens and enter said detector system;
c. providing a material system to said means for supporting a material system, the composition of said material system being sufficiently well known so that retardance entered thereby to a polarized beam of electromagnetic radiation of a given wavelength, which is caused to interact with said material system in a plane of incidence thereto, can be accurately modeled mathematically by a parameterized equation which, when parameters therein are properly evaluated, allows calculation of retardance entered thereby between orthogonal components of a beam of electromagnetic radiation caused to interact therewith in a plane of incidence thereto, given wavelength;
d. providing a mathematical model for said ellipsometer system and said input and output lenses and said material system, comprising separate parameterized equations for independently calculating retardance entered between orthogonal components of a beam of electromagnetic radiation caused to pass through each of said input and output lenses and interact with said material system in a plane of incidence thereto; such that where parameters in said mathematical model are properly evaluated, retardance entered between orthogonal components of a beam of electromagnetic radiation which passes through each of said input and output lenses and interacts with said material system in a plane of incidence thereto can be independently calculated from said parameterized equations, given wavelength;
e. obtaining a spectroscopic set of ellipsometric data with said parameterizable material system present on the means for supporting a material system, utilizing a beam of electromagnetic radiation provided by said source of electromagnetic radiation, said beam of electromagnetic radiation being caused to pass through said input lens, interact with said parameterizable material system in a plane of incidence thereto, and exit through said output lens and enter said detector system;
f. by utilizing said mathematical model provided in step d. and said spectroscopic set of ellipsometric data obtained in step e., simultaneously evaluating parameters in said mathematical model parameterized equations for independently calculating retardance entered between orthogonal components in a beam of electromagnetic radiation caused to pass through said input lens, interact with said material system in a plane of incidence thereto, and exit through said output lens.
The end result of practice of said method is that application of said parameterized equations for each of said input lens, output lens and material system for which values of parameters therein have been determined in step f., enables independent calculation of retardance entered between orthogonal components of a beam of electromagnetic radiation by each of said input and output lenses, and said material system, at given wavelengths in said spectroscopic set of ellipsometric data. And, it is emphasized that said calculated retardance values for each of said input lens, output lens and material system are essentially uncorrelated.
It is further to be appreciated that one of said input or output lenses can be physically absent entirely, which is the equivalent to considering it to be simply surrounding ambient atmosphere with associated non-birefringent properties. The language “providing spatially separated input and output lenses, at least one of said input and output lenses demonstrating birefringence when a beam of electromagnetic radiation is caused to pass therethrough”, is to be interpreted to include such a situation wherein a non-birefringent lens is simply atmospheric ambient or an optical equivalent. Additionally, it is to be understood that input optical elements can comprise beam directing means and window(s), (as in a vacuum chamber), in addition to input lens(es); and that output optical elements can comprise selection beam directing means and window(s), (as in a vacuum chamber), as well as output lens(es).
As further discussed later herein, a modification to the just recited method can be to, (in the step d. provision of a mathematical model for said ellipsometer system and said input and output lenses and said parameterizable material system for each of said input and output lenses), provide separate parameterized mathematical model parameterized equations for retardance entered to each of said two orthogonal components of a beam of electromagnetic radiation caused to pass through said input and output lenses. When this is done, at least one of said orthogonal components for each of said input and output lenses is directed out of the plane of incidence of said electromagnetic beam onto said parameterizable material system. And, typically, though not necessarily, one orthogonal component will be aligned with the plane of incidence of said electromagnetic beam onto said parameterizable material system. When this is done, calculation of retardation entered between orthogonal components of said beam of electromagnetic radiation, given wavelength, by said input lens is provided by comparison of retardance entered to each of said orthogonal components for said input lens, and such that calculation of retardation entered between orthogonal components of said beam of electromagnetic radiation, given wavelength, by said output lens is provided by comparison of retardance entered to each of said orthogonal components for said output lens.
It is pointed out that the step f. simultaneous evaluation of parameters in said mathematical model parameterized equations for said parameterizable material system, and for said input and output lenses, is typically, though not necessarily, achieved by a square error reducing mathematical curve fitting procedure.
It is important to understand that in the method recited earlier, the step b. positioning of an ellipsometer system source of electromagnetic radiation and an ellipsometer system detector system includes positioning a polarizer between said source of electromagnetic radiation and said input lens, and the positioning of an analyzer between said output lens and said detector system, and in which the step e. obtaining of a spectroscopic set of ellipsometric data typically involves obtaining data at a plurality of settings of at least one component selected from the group consisting of: (said analyzer and said polarizer). As well, it is to be understood that additional elements can also be placed between said source of electromagnetic radiation and said input lens, and/or between said output lens and said detector system, and that the step e. obtaining of a spectroscopic set of ellipsometric data can involve, alternatively or in addition to the recited procedure, obtaining data at a plurality of settings of at least one of said additional components.
It is also to be understood that the step of providing separate parameterized mathematical model parameterized equations for enabling independent calculation of retardance entered by said input said output lenses between orthogonal components of a beam of electromagnetic radiation caused to pass through said input and output lenses preferably involves parameterized equations having a form selected from the group consisting of:ret(λ)=(K1/λ)ret(λ)=(K1/λ)*(1+(K2/λ2))ret(λ)=(K1/λ)*(1+(K2/λ2)+(K3/λ4))
A modified method of accurately evaluating parameters in parameterized equations in a mathematical model of a system of spatially separated input and output lenses, said parameterized equations enabling, when parameters therein are properly evaluated, independent calculation of retardation entered by each of said input lens and said output lens to at least one orthogonal component(s) of a beam of electromagnetic radiation caused to pass through said input and output lenses, at least one of said input and output lenses being birefringent, said method comprising, in a functional order, the steps of:
a. providing spatially separated input and output lenses, at least one of said input and output lenses demonstrating birefringence when a beam of electromagnetic radiation is caused to pass therethrough, there being a means for supporting a material system positioned between said input and output lenses;
b. positioning an ellipsometer system source of electromagnetic radiation and an ellipsometer system detector system such that in use a beam of electromagnetic radiation provided by said source of electromagnetic radiation is caused to pass through said input lens, interact with said material system in a plane of incidence thereto, and exit through said output lens and enter said detector system;
c. providing a material system to said means for supporting a material system;
d. providing a mathematical model for said ellipsometer system and said input and output lenses and said material system, comprising, for each of said input lens and said output lens, separate parameterized equations for retardance for at least one orthogonal component in a beam of electromagnetic radiation provided by said source of electromagnetic radiation, which orthogonal component is directed out of a plane of incidence which said electromagnetic beam makes with said material system in use, and optionally providing separate parameterized equations for retardance for an in-plane orthogonal component of said beam of electromagnetic radiation, such that retardation entered to said out-of-plane orthogonal component, and optionally to said in-plane orthogonal component, of said beam of electromagnetic radiation by each of said input and output lenses, can, for each of said input and output lenses, be separately calculated by said parameterized equations, given wavelength, where parameters in said parameterized equations are properly evaluated;
e. obtaining a spectroscopic set of ellipsometric data with said material system present on the means for supporting a material system, utilizing a beam of electromagnetic radiation provided by said source of electromagnetic radiation, said beam of electromagnetic radiation being caused to pass through said input lens, interact with said material system in a plane of incidence thereto, and exit through said output lens and enter said detector system;
f. by utilizing said mathematical model provided in step d. and said spectroscopic set of ellipsometric data obtained in step e., simultaneously evaluating material system DELTA'S in correlation with in-plane orthogonal component retardation entered to said beam of electromagnetic radiation by each of said input and output lenses, and parameters in said mathematical model parameterized equations for out-of-plane retardance entered by said input lens and said output lens to a beam of electromagnetic radiation caused to pass through said input lens, interact with said material system in said plane of incidence thereto, and exit through said output lens.
Again, application of said parameterized equations for out-of-plane retardance entered by said input lens and said output lens to a beam of electromagnetic radiation caused to pass through said input lens, interact with said material system in said plane of incidence thereto, and exit through said output lens, for which values of parameters therein are determined in step f., enables independent calculation of retardance entered to said out-of-plane orthogonal component of a beam of electromagnetic radiation by each of said input and output lenses, given wavelength.
Also, again the step f. simultaneous evaluation of parameters in said mathematical model parameterized equations for calculation of retardance entered to said out-of-plane orthogonal component of a beam of electromagnetic radiation by each of said input and output lenses, given wavelength, and said correlated material system DELTA'S and retardance entered to said in-plane orthogonal component of a beam of electromagnetic radiation by each of said input and output lenses, is typically achieved by a square error reducing mathematical curve fitting procedure.
It remains, in said method, to definitely provide values for parameters in the in-plane parameterized equations for retardation, in said mathematical model of a system of spatially separated input and output lenses. Said method therefore further comprises the steps of:
g. providing a parameterized equation for retardation entered by said material system to the in-plane orthogonal component of a beam of electromagnetic radiation, and as necessary similar parameterized equations for retardation entered by each of said input and output lenses to the in-plane orthogonal component of a beam of electromagnetic radiation; and
h. by utilizing said parameterized mathematical model provided in step d. and said spectroscopic set of ellipsometric data obtained in step e., simultaneously evaluating parameters in said mathematical model parameterized equations for independent calculation of retardance entered in-plane by said material system and by said input lens and said output lens such that the correlation between material system DELTA'S and the retardance entered by said in-plane orthogonal component of a beam of electromagnetic radiation by each of said input and output lenses, at given wavelengths in said spectroscopic set of ellipsometric data, is broken.
The end result of practice of the immediately foregoing steps a.-h. is that application of said parameterized equations for each of said input lens, output lens and material system for which values of parameters therein have been determined in step h., enables independent calculation of retardance entered to both said out-of-plane and said in-plane orthogonal components of a beam of electromagnetic radiation by each of said input and output lenses, and retardance entered by said material system to said in-plane orthogonal component of said beam of electromagnetic radiation, at given wavelengths in said spectroscopic set of ellipsometric data.
As before for other parameter evaluation steps, the step h. simultaneous evaluation of parameters in said mathematical model parameterized equations for said in-plane retardation entered by said parameterized material system, and said input and output lenses, is typically achieved by a square error reducing mathematical curve fitting procedure.
If the material system present can not be easily parameterized, said method of accurately evaluating parameters in parameterized equations in a mathematical model of a system of spatially separated input and output lenses, provides that the following steps, g.-j. be practiced:
g. removing the material system from said means for supporting a material system positioned between said input and output lenses, and positioning in its place an alternative material system for which a parameterized equation for calculating in-plane retardance entered to a beam of electromagnetic radiation, given wavelength, can be provided;
h. providing a parameterized equation for retardation entered in-plane to an orthogonal component of a beam of electromagnetic radiation by said alternative material system which is then positioned on said means for supporting a material system positioned between said input and output lenses, and as necessary similar parameterized equations for retardation entered by each of said input and output lenses to the in-plane orthogonal component of a beam of electromagnetic radiation;
i. obtaining a spectroscopic set of ellipsometric data with said alternative material system present on the means for supporting a material system, utilizing a beam of electromagnetic radiation provided by said source of electromagnetic radiation, said beam of electromagnetic radiation being caused to pass through said input lens, interact with said alternative material system in a plane of incidence thereto, and exit through said output lens and enter said detector system;
j. by utilizing said parameterized mathematical model for said input lens and said output lens provided in step d. and said parameterized equation for retardation entered by said alternative material system provided in step h., and said spectroscopic set of ellipsometric data obtained in step i., simultaneously evaluating parameters in said mathematical model parameterized equations for independent calculation of retardance entered to an in-plane orthogonal component of said beam of electromagnetic radiation by said alternative material system and by said input lens and said output lens, such that correlation between DELTA'S entered by said alternative material system and retardance entered by said in-plane orthogonal component of said beam of electromagnetic radiation, by each of said input and output lenses, at given wavelengths in said spectroscopic set of ellipsometric data, is broken, said simultaneous evaluation optionally providing new values for parameters in parameterized equations for calculation of retardance entered in said out-of-plane components of said beam of electromagnetic radiation by each of said input lens and said output lens;
The end result being that application of said parameterized equations for each of said input lens and output lens and alternative material system, for each of which values of parameters therein have been determined in step j., enables independent calculation of retardance entered to both said out-of-plane and said in-plane orthogonal components of a beam of electromagnetic radiation by each of said input lens and said output lens, and retardance entered by said alternative material system to said in-plane orthogonal component of a beam of electromagnetic radiation, at given wavelengths in said spectroscopic set of ellipsometric data.
As before, said method of accurately evaluating parameters in parameterized equations in a mathematical model of a system of spatially separated input and output lenses provides that in the step j. simultaneous evaluation of parameters in said mathematical model parameterized equations for said in-plane retardation entered by said parameterized material system, and at least said in-plane input lens and output lens, is typically achieved by a square error reducing mathematical curve fitting procedure.
As mentioned with respect to the first method disclosed above, said method of accurately evaluating parameters in parameterized equations in a mathematical model of a system of spatially separated input and output lenses also provides that the step b. positioning of an ellipsometer system source of electromagnetic radiation and an ellipsometer system detector system includes positioning a polarizer between said source of electromagnetic radiation and said input lens, and the positioning of an analyzer between said output lens and said detector system, and in which the step e. obtaining of a spectroscopic set of ellipsometric data involves obtaining data at a plurality of settings of at least one component selected from the group consisting of: (said analyzer and said polarizer). As well, it is again to be understood that additional elements can also be placed between said source of electromagnetic radiation and said input lens, and/or between said output lens and said detector system, and that the step e. obtaining of a spectroscopic set of ellipsometric data can involve, alternatively or in addition to the recited procedure, obtaining data at a plurality of settings of at least one of said additional components.
Said method of accurately evaluating parameters in parameterized equations in a mathematical model of a system of spatially separated input and output lenses also provides that the step of providing separate parameterized mathematical model parameterized equations for enabling independent calculation of out-of-plane and in-plane retardance entered by said input said output lenses to said beam of electromagnetic radiation caused to pass through said input and output lenses involve parameterized equations having a form selected from the group consisting of:ret(λ)=(K1/λ)ret(λ)=(K1/λ)*(1+(K2/λ2))ret(λ)=(K1/λ)*(1+(K2/λ2)+(K3/λ4))
It is again noted that while said method can be practiced with any type “lenses”, be there one or two of them, (ie. one, or both, of the input or output lenses can be essentially non-birefringent and even ambient), and while an input lens or output lens can be considered to be formed by a plurality of elements, (eg. two elements made of different materials such as Fused Silica and Calcium Fluoride), the step a. providing of spatially separated input and output lenses is best exemplified as being practiced by the providing of an ellipsometer system that has both input and output lenses present therein through which an beam of electromagnetic radiation is caused to convergently enter and exit in a recolliminated form, receptively.
Any of the described methods can further involve, in a functional order, the following steps a1.-a4:
a1. fixing evaluated parameter values in mathematical model parameterized equations, for each of said input lens and output lens, such that said parameterized equations allow independent determination of retardation entered between orthogonal components of a beam of electromagnetic radiation caused to pass through said input and output lenses, given wavelength; and
a2. causing an unknown material system to be present on said means for supporting a material system;
a3. obtaining a spectroscopic set of ellipsometric data with said unknown material system present on the means for supporting a material system, utilizing a beam of electromagnetic radiation provided by said source of electromagnetic radiation, said beam of electromagnetic radiation being caused to pass through said input lens, interact with said alternative material system in a plane of incidence thereto, and exit through said output lens and enter said detector system; and
a4. by utilizing said mathematical model for said input lens and said output lens in which parameter values in mathematical model parameterized equations, for each of said input lens and output lens have been fixed, simultaneously evaluating PSI'S and uncorrelated DELTA'S parameters for said unknown material system.
As in other steps in said method in which parameter values are evaluated, it is again noted that the method of accurately evaluating parameters in parameterized equations in a mathematical model of a system of spatially separated input and output lenses in which said simultaneous evaluation of PSI'S and DELTA'S for said unknown material are typically achieved by a square error reducing mathematical curve fitting procedure.
As alluded to earlier, the step of providing spatially separated input and output lenses, at least one of said input and output lenses demonstrating birefringence when a beam of electromagnetic radiation is caused to pass therethrough, can involve one or both lens(es) which is/are not birefringent. And, said at least one lens which is not birefringent can be essentially a surrounding ambient, (ie. a phantom lens which is essentially just the atmosphere surrounding a material system).
It is noted that where parameters in parameterized equations for out-of-plane retardance equations have been determined, a focused version of the method for accurately evaluating parameters in parameterized equations in a mathematical model of a system of spatially separated input and output lenses can comprise the steps of b1-b7:
b1. fixing evaluated parameter values in mathematical model parameterized equations, for each of said input lens and output lens, such that said parameterized equations allow independent determination of retardation entered between orthogonal components of a beam of electromagnetic radiation caused to pass through said input and output lenses, given wavelength; and
b2. causing an unknown material system to be present on said means for supporting a material system;
b3. obtaining a spectroscopic set of ellipsometric data with said unknown material system present on the means for supporting a material system, utilizing a beam of electromagnetic radiation provided by said source of electromagnetic radiation, said beam of electromagnetic radiation being caused to pass through said input lens, interact with said alternative material system in a plane of incidence thereto, and exit through said output lens and enter said detector system; and
b4. by utilizing said mathematical model for said input lens and said output lens in which parameter values in mathematical model parameterized equations, for each of said input lens and output lens have been fixed, simultaneously evaluating ALPHA'S and BETA'S for said unknown material system, (see the Detailed Description for definition of ALPHA'S and BETA'S);
b5. applying transfer functions to said simultaneously evaluated ALPHA'S and BETA'S for said unknown material system to the end that a data set of effective PSI's and DELTA's for a combination of said lenses and said material system is provided;
b6. providing a mathematical model for said combination of said lenses and said material system which separately accounts for the retardation effects of the presence of said lenses and said material system by parameterized equations; and
b7. by utilizing said mathematical model for said combination of said lenses and said material system which separately accounts for the effects of the presence of at least said lenses by parameterized equations; and said data set of effective PSI's and DELTA's for a combination of said lenses and said material system, simultaneously evaluating actual PSI's and DELTA's for said unknown material system per se.
In the case, for instance, where the ellipsometer involved is a Rotating Analyzer, or Rotating Polarizer ellipsometer system, (but not where the ellipsometer involved is a Rotating Compensator System), it is noted that determination of “Handedness” is required. Therefore the foregoing method can include, as necessary, providing a mathematical model for said combination of said lenses and said material system which separately accounts for the retardation effects of the presence of said lenses and said material system by parameterized equations which further includes providing for the effects of Handedness. It is specifically stated that where the approach of regressing onto effective PSI and DELTA values, (as determined in step b7.), is utilized, the mathematical model can be derived so that “Handedness” is accounted for in arriving at actual PSI's and DELTA's for said unknown material system per se.
As a general comment it is to be understood that separate PSI and DELTA values are achieved for each angle of incidence a beam of electromagnetic radiation makes with respect to a material substrate and for each wavelength utilized in a spectroscopic range of wavelengths.
Also, as said methodology finds application in ellipsometer systems in which are present input and/or output lenses, the foregoing methods of use are recited utilizing specific reference to input and output lenses in ellipsometer systems. In general said methodology can be applied where any input and/or output optical elements are present.
While the forgoing has presented method steps in a logical sequence to enhance disclosure, it is to be understood that the steps of any method recitation in this Specification can be practiced in any functional order.
Patents which specifically focus on the use of lenses, preferrably achromatic, in ellipsometry and related systems are:
U.S. Pat. Nos. 5,877,859 and 5,798,837 to Aspnes et al.;
U.S. Pat. No. 5,333,052 to Finarov;
U.S. Pat. No. 5,608,526 to Piwonka-Corle et al.;
U.S. Pat. No. 5,793,480 to Lacy et al.;
U.S. Pat. Nos. 4,636,075 and 4,893,932 to Knollenberg; and
U.S. Pat. No. 4,668,860 to Anthon.
U.S. Pat. No. 5,917,594 to Norton.
U.S. Pat. No. 5,166,752 to Spanier et al.
U.S. Pat. No. 6,493,097 to Ivarsson is disclosed as it describes an imaging ellipsometer which comprises a two dimensional array detector.
U.S. Pat. No. 5,596,406 to Rosencwaig et al., is disclosed as it describes an ellipsometer which comprises a two dimensional array.
Published Patent Application No. US2002/0163634 by Meeks et al. is disclosed as it describes controlling spot size in profilometer, ellipsometer, reflectometer and scatterometer.
Patent to Johs et al., U.S. Pat. No. 5,936,734, describes the use a beam of electromagnetic radiation to investigate a sample which has a plurality of regions which have thin films of different relative thicknesses, and/or are comprised of different materials, is complicated by the fact that components of said beam reflected by different regions of this sample can add in two different modes, namely coherent and incoherent. Said 734 patent taught that a partition parameter, which accounted for the percentage of a reflected beam that adds coherently and incoherently, should be a part of the mathematical model of the sample and system used to do the analysis. Many other references exist which describe similar difficulties which arise when using electromagnetic radiation to investigate non-homogeneous samples.
PCT Application WO 01/086257 describes use of an aperture and lens to define spot size of a beam of electromagnetic radiation on a sample.
A paper by Johs, titled “Regression Calibration Method for Rotating Element Ellipsometers”, Thin Solid Films, 234 (1993) is also disclosed as it describes a mathematical regression based approach to calibrating ellipsometer systems, including characterizing a sample.
It is further disclosed that the bi-lateral slit assembly of Co-owned U.S. Pat. No. 5,661,589 is revisited as part of the presently disclosed invention. Further, the disclosed invention includes in some embodiments a multiple detector system as disclosed in Allowed application Ser. No. 09/531,877, (now U.S. Pat. No. 6,535,286), from which this application Continues-in-Part via Co-Pending application Ser. No. 10/376,677, Filed Feb. 28, 2003.
Spectroscopic ellipsometry (SE) was developed in the early 1970's after single wavelength ellipsometry had gained widespread acceptance. The first (SE) systems provided limited Ultraviolet (UV) to near Infrared (IR) spectral range capability, and with the exception of a few research instruments, this remained the case until the 1990's. Many challenges faced development of (VUV) ellipsometer systems, including the fact that many optical element materials absorb in the (VUV) wavelength range. Vacuum Ultraviolet (VUV) ellipsometry was so named as it was initially carried out in vacuum, however, the terminology is today applied where purging gas such as nitrogen or argon is utilized in place of vacuum at wavelengths, typically with an energy less than about 10 ev. The reason (VUV) ellipsometry must be carried out in vacuum or purging gas is that (VUV) wavelengths, are absorbed by oxygen and water vapor.
In the mid-1980's a Spectroscopic ellipsometer was constructed at the BESSY Synchrotron in Berlin for application in the (VUV) wavelength range, (eg. 5-35 eV), and in the 1990's Spectroscopic ellipsometry was achieved in the Extreme Ultraviolet (EUV) range, (eg. greater than 35 eV), at KEK-PF. Application of ellipsometry in the (VUV) and (EUV) wavelength ranges remained restricted to said research facilities until in 1999 commercial (VUV) ellipsometer systems became available from companies such as the J.A. Woollam Co. Inc. At present there are approximately twenty-five (VUV) Systems in use worldwide. It is noted that commercial (VUV) instruments, which provided wavelengths down to 146 nm, were introduced in response to the need for bulk material properties at 156 nm, which is utilized in lithography as applied to semiconductor gate oxide production.
The practice of ellipsometry, polarimetry, spectrophotometry, reflectometry, scatterometry and the like, using Infrared (IR), (eg. 2-33 micron), and Ultraviolet (UV), (eg. 135-1700 nm), Electromagnetic Radiation Wavelengths, then is, as disclosed above, known. As mentioned, electromagnetic Radiation with wavelengths below about 190 nm is absorbed by atmospheric components such as Oxygen and Water Vapor. Thus, practice of Ellipsometry etc. using VUV Wavelengths is typically carried out in vacuum or an atmosphere which does not contain oxygen and/or water vapor or other absorbing components. The J.A. Woollam CO. VUV-VASE, (Registered Trademark), for instance, utilizes a Chamber which encompasses a substantially enclosed space which during use is purged by Nitrogen and/or Argon or functionally equivalent gas. (Note Nitrogen does not significantly absorb UV Range wavelengths above about 130 nm, and Argon is in some respects even a better choice as it has an even lower yet onset of UV Range wavelength absorption). Further, the source of the electromagnetic radiation in the J.A. Woollam CO. VUV-VASE is preferably a Deuterium Lamp or a Xenon Lamp present within a J.A. Woollam Co. monochromator system which produces wavelengths of 115-400 nm, (of which 135-190 nm is used), and up to about 2000 nm, respectively. Specific wavelengths are selected by said J.A. Woollam Co. Monochromator which comprises a specially designed Cherny-Turner Spectrometer.
It is beneficial to note that Spectroscopic Ellipsometry (SE) is practiced utilizing an ellipsometer system generally comprising:                a source system comprising:                    a source of electromagnetic radiation: and            a polarization state modifier system:                        a stage for supporting a sample system;        a plurality of polarization state detector systems, each of which comprises:                    a polarization state analyzer: and            a detector system;such that a beam of electromagnetic radiation is produced by said source of electromagnetic radiation and caused to pass through said polarization state modifier system, interact with a sample system placed on said stage for supporting a sample system, pass through a polarization state analyzer and enter a detector system in the pathway thereof. It is noted that the terminology “a source” can include multiple sources which serve to provide a beam of electromagnetic radiation in different wavelength ranges.                        
The standard J.A. Woollam CO. VUV-VASE Spectroscopic Ellipsometer system sequentially comprises, mounted inside substantially enclosed space within a Chamber:                a monochromator;        a beam polarizing means;        a polarization state modifying means as described in U.S. Pat. Nos. 5,956,145 and 5,757,494;        a beam alignment detector means such as a quad detector as mentioned in U.S. Pat. No. 5,872,630 in Col. 20, Lines 55-57;        a stage for supporting a sample system;        an analyzing means; and        data detector means;wherein said monochromator comprises;        a) source of electromagnetic radiation;        b) a first slit in a first slit providing means;        c) a first mirror;        d) a first stage comprising a plurality of gratings, each of which can be rotated into a functional position;        e) a second mirror;        f) a second slit in said second slit providing means;        g) a third mirror        h) a second stage comprising a plurality of gratings, each of which can be rotated into a functional position;        i) a fourth mirror;        j) order sorting filter means;        k) a pin hole;with a beam chopper being present after said source of electromagnetic radiation, (typically, but not necessarily, just prior to said pin hole).        
In use an electromagnetic beam from said source of the electromagnetic radiation is:                caused to pass through said first slit;        reflect from said first mirror;        interact with one of said plurality of gratings on said first stage which is rotated into a functional position;        reflect from said second mirror;        pass through said second slit;        reflect from said third mirror;        interact with one of said plurality of gratings on said second stage which is rotated into a functional position;        reflect from said fourth mirror; and        proceed through order sorting filtering means;        with monochromator selected wavelengths being caused to exit through said pinhole.        
The beam is also chopped by beam chopping means placed somewhere after the source of electromagnetic radiation, (typically, but not necessarily, just before the pin hole providing means).
The gratings on said first and second stages are independently rotated into precise desired functional positions via stepper motors controlled by computer. This has proven to provide superior precision and repeatability than commercially available grating positioning systems, at least in part because the J.A. Woollam Co. system does not control one grating supporting stage as a slave to the other, as is done in known competing systems. Again, in use, the stages which support the gratings are independently rotated to optimum orientations.
Further, it is disclosed that an electromagnetic radiation beam produced by said J.A. Woollam CO. Monochromator has been shown to provide a highly collimated beam, with typical defining parameters being a 5 mm diameter at the pinhole output of the Monochromator, with divergence to about 20 mm diameter at 20 Feet, (ie. 6000 mm). This represents a divergence angle of only about 0.00125 radians, (ie. 0.07 Degrees). The collimating optics comprises a spherical mirror in the optical path after the pinhole. Said spherical mirror collimates the beam and directs it to a flat folding mirror, and said flat folding mirror directs the beam out of the monochromator.
While not new, it is noted that alignment of the Xenon Lamp follows a two step procedure. First it must be understood that the Xenon Lamps used have an Ellipsoidal Reflector associated therewith, which has a focal length and major and minor axes. The first step is to place the Xenon Lamp into the focal length position. This is followed by adjusting the major axis of the Ellipsoidal Reflector to be in line with the First Slit. The alignment procedure is typically monitored by maximizing intensity output from the Pin Hole.
It is also noted that the Deuterium and/or Xenon sources of electromagnetic radiation can be placed as indicated, but separate from the other components of the monochromator. For instance, in an ellipsometer system which sequentially comprises the Deuterium and/or Xenon sources in a Polarization State Generation System (PSG), a Sample System supporting Stage and a Polarization State Detector System (PSD), the components other than the Source of Electromagnetic Radiation can be placed in any functional location before or after the Sample System between the (PSG) and (PSD) or within one and/or the other.
Continuing, problems have been identified with application of the J.A. Woollam Co. monochromator system sold to date in that electrical wiring and motor driver electronic components have been included inside the substantially enclosed space in which specific wavelengths in electromagnetic beams are selected. As mentioned, outgassing from anything inside said substantially enclosed space can require very long periods of time, and substantial purging can be required where Vacuum-Ultraviolet (VUV) wavelengths are utilized. Further, diminished throughput of electromagnetic radiation with time has been traced to be, at least in part, caused by deposition and polymerization of polymers present in wire coatings on optical surfaces such as the surfaces of the mirrors and gratings inside the substantially enclosed space. It is also identified that electrical connections to components, such as the means for providing the first and second slits and rotation effecting means for the first and second grating stages, and the Lamp selecting mirror have, to date, been hard wired inside the enclosing means, thereby making replacement tedious. Further, the position of electromagnetic radiation source means present inside said substantially enclosed space must be adjusted to provide a beam which follows an intended locus. To date, position adjustments have required opening the enclosing means, thereby requiring additional purging where UV wavelengths are utilized.
Known patents include U.S. Pat. No. 5,303,035 to Ludcke et al., which describes a precision micropositioner that allows up to six degrees of motion freedom which are adjustable from controls located in a single plane. The mechanism involves forcing balls between support and ramped elements. It is noted that the range of adjustment is limited by the slope and length of the ramped elements. Specifically the present invention enables a greater range of adjustment. Other patents which describe the use of balls to transmit motion include U.S. Pat. No. 6,042,298 to Mastrogiannis et al. which describes the use of two sequences of balls oriented in manner so that forcing a wedge shape between the first ball in each sequence causes coupling of a joint between two sections in a frame. U.S. Pat. No. 4,656,780 to Miyauchi et al. describes an apparatus for reciprocally moving an object involving a string of interconnected balls. U.S. Pat. No. 4,062,251 to Parsons describes a sequence of interconnected balls in a ball cage, for the purpose of transmitting motion. U.S. Pat. No. 3,204,480 to Bradbury describes a motion transmitting means, again using a sequence of interconnected balls. U.S. Pat. No. 1,807,914 to Hopkins describes a lifting jack which incorporates use of a sequence of balls to transmit motion.
U.S. Pat. No. 6,414,302 B1 to Freeouf is identified as it describes use of VUV wavelengths which range up through 10 eV in systems which are used to investigate properties of solids.
Known patents pertaining to Multiple Detector Systems include a patent to Briggs, U.S. Pat. No. 3,405,270 describing a system containing slots which allow positioning of a source and detector relative to one another. A patent to Rayton et al., U.S. Pat. No. 1,773,436 describes a polarization photometer system with a bracket arm rotatable secured to a post, which is used to support a table and test specimen. U.S. Pat. No. 4,242,581 to Crow, describes a system of four laser energy detectors arranged to allow simultaneous energy monitoring, which system can be easily positioned with respect to a laser beam source aperture. U.S. Pat. No. 3,630,621 to Liskowitz provides a system for measurement of visibility through a fluid using polarized light wherein a source and a detector which are easily positioned with respect to one another. Other patents identified, but not felt to be particularly relevant are U.S. Pat. No. 4,938,602 to May et al., and U.S. Pat. No. 5,494,829 to Sandstrom et al. Patents identified by the Examiner in prosecution of the patent application Ser. No. 09/531,877, filed Mar. 21, 2000 include patent to Green et al. U.S. Pat. No. 5,956,145, patent to Johs et al. No. 6,353,477, patent to Rosencwaid et al. U.S. Pat. No. 6,278,519, patent to Herzinger et al. U.S. Pat. No. 6,084,675, previously identified patent to Johs et al. U.S. Pat. No. 5,872,630, patent to Drevillion et al., U.S. Pat. No. 5,557,671 and patent to Spanier et al., U.S. Pat. No. 5,166,752.
The disclosed invention provides improvements to the existing J.A. Woollam Co. monochromator system which are aimed at overcoming the identified problems.
Patents of general interest of which the Inventor is aware include those to:                Woollam et al, U.S. Pat. No. 5,373,359,        Johs et. al. U.S. Pat. No. 5,666,201        Green et al., U.S. Pat. No. 5,521,706,        Johs et al., U.S. Pat. No. 5,504,582and are disclosed for general information as they pertain to ellipsometer systems.        
Further patents of which the Inventor is aware include:
U.S. Pat. Nos. 5,757,494 and 5,956,145 to Green et al., in which are taught a method for extending the range of Rotating Analyzer/Polarizer ellipsometer systems to allow measurement of DELTA'S near zero (0.0) and one-hundred-eighty (180) degrees, and the extension of modulator element ellipsometers to PSI'S of forty-five (45) degrees. Said patents describes the presence of a variable, transmissive, bi-refringent component which is added, and the application thereof during data acquisition to enable the identified capability.
U.S. Pat. No. 5,706,212 to Thompson et al. is also disclosed as it teaches a mathematical regression based double Fourier series ellipsometer calibration procedure for application, primarily, in calibrating ellipsometers system utilized in infrared wavelength range. Bi-refringent, transmissive window-like compensators are described as present in the system thereof, and discussion of correlation of retardations entered by sequentially adjacent elements which do not rotate with respect to one another during data acquisition is described therein.
Patent to He et al., U.S. Pat. No. 5,963,327 is disclosed as it describes an ellipsometer system which enables providing a polarized beam of electromagnetic radiation at an oblique angle-of-incidence to a sample system in a small spot area.
Patent to Johs et al., U.S. Pat. No. 5,872,630 is disclosed as it describes an ellipsometer system in which an analyzer and polarizer are maintained in a fixed in position during data acquisition, while a compensator is caused to continuously rotate.
Patent to Dill et al., U.S. Pat. No. 4,953,232 is disclosed as it describes a rotating compensator ellipsometer system.
Patents disclosed as they Claim various Compensator Designs are:                U.S. Pat. No. 5,946,098 to Johs et al.;        U.S. Pat. No. 5,963,325 to Johs et al.;        U.S. Pat. No. 6,084,674 to Johs et al.;        U.S. Pat. No. 6,084,675 to Herzinger et al.;        U.S. Pat. No. 6,100,981 to Johs et al.;        U.S. Pat. No. 6,118,537 to Johs et al.;        U.S. Pat. No. 6,141,102 to Johs et al.        
U.S. Pat. No. 4,556,292 to Mathyssek et al. and
U.S. Pat. No. 5,475,525 to Tournois et al.;
are disclosed as they were cited in examination of some of the just disclosed patents.
Patent to Coates et al., U.S. Pat. No. 4,826,321 is disclosed as it describes applying a reflected monochromatic beam of plane polarized electromagnetic radiation at a Brewster angle of incidence to a sample substrate to determine the thickness of a thin film thereupon. This patent also describes calibration utilizing two sample substrates, which have different depths of surface coating.
Other patents which describe use of reflected electromagnetic radiation to investigate sample systems are:                RE 34,783, U.S. Pat. Nos. 4,373,817, and 5,045,704 to Coates.        
Patent to Bjork et al., U.S. Pat. No. 4,647,207 is disclosed as it describes an ellipsometer system which has provision for sequentially positioning a plurality of reflective polarization state modifiers in a beam of electromagnetic radiation. While said 207 patent mentions investigating a sample system in a transmission mode, no mention or suggestion is found for utilizing a plurality of transmitting polarization state modifiers. Patent Nos.:                U.S. Pat. No. 4,210,401;        U.S. Pat. No. 4,332,476; and        U.S. Pat. No. 4,355,903;are also identified as being cited in the 207 patent. It is noted that systems as disclosed in these patents, (particularly in the 476 patent), which utilize reflection form an element to modify a polarization state can, if such an element is an essential duplicate of an investigated sample and is rotated ninety degrees therefrom, the effect of the polarization state modifying element on the electromagnetic beam effect is extinguished by the sample.        
Patent to Mansuripur et al., U.S. Pat. No. 4,838,695 is disclosed as it describes an apparatus for measuring reflectivity.
Patents to Rosencwaig et al., Nos.:                U.S. Pat. No. 4,750,822; and        U.S. Pat. No. 5,595,406are also identified as they describe systems which impinge electromagnetic beams onto sample systems at oblique angles of incidence. The 406 patent provides for use of multiple wavelengths and multiple angles of incidence. For similar reasons Patent No.:        U.S. Pat. No. 5,042,951to Gold et al. is also disclosed.        
Patent to Osterberg, U.S. Pat. No. 2,700,918 describes a microscope with variable means for increasing the visibility of optical images, partially comprised of discrete bi-refringent plates which can be positioned in the pathway between an eyepiece and an observed object. Other patents identified in a Search which identified said 918 patent are Nos.:                U.S. Pat. No. 3,183,763 to Koester;        U.S. Pat. No. 4,105,338 to Kuroha;        U.S. Pat. No. 3,992,104 to Watanabe;and a Russian Patent, No. SU 1518728. Said other patents are not believed to be particularly relevant, however.        
U.S. Pat. No. 5,329,357 to Bernoux et al. is also identified as it Claims use of fiber optics to carry electromagnetic radiation to and from an ellipsometer system which has at least one polarizer or analyzer which rotates during data acquisition. It is noted that if both the polarizer and analyzer are stationary during data acquisition that this patent is not controlling where electromagnetic radiation carrying fiber optics are present.
U.S. Pat. No. 6,628,917 to Johs is disclosed as present invention preferred practice is to utilize a spectroscopic source of electromagnetic radiation with a relatively flat spectrum over a large range of wavelengths.
Patent to Chen et al., U.S. Pat. No. 5,581,350, is disclosed as it describes a method for regression calibration of ellipsometers.
U.S. Pat. No. 6,608,526 to Piwonka-Corle et al is disclosed, as is
U.S. Pat. No. 5,596,411 to Fanton et al.,
as the Applicant is aware thereof.
Patents which focus on the use of Lenses in Ellipsometer Systems are:                U.S. Pat. Nos. 5,877,859 and 5,798,837 to Aspnes et al.;        U.S. Pat. No. 5,333,052 to Finarov;        U.S. Pat. No. 5,608,526 to Piwonka-Corle et al.;        U.S. Pat. No. 5,793,480 to Lacy et al.;        U.S. Pat. Nos. 4,636,075 and 4,893,932 to Knollenberg; and        U.S. Pat. No. 4,668,860 to Anthon.        Patent found is U.S. Pat. No. 5,917,594 to Norton is the most relevant the system disclosed therein utilizes a spherical mirror to focus an electromagnetic beam onto the surface of a sample in the form of a small spot.        